The present invention relates to data communications in packet switched networks and more specifically to the mobility of terminals in networks implementing the Mobile Internet Protocol (MIP).
Typical IP networks are mainly developed for stationary terminals connected to the network by wired connections. Mobile terminals may be connected by use of base transceiver stations, but to achieve true mobility functions are required for handling e.g. roaming and handover in the network.
The Mobile-IP working group of the Internet Engineering Task Force (IETF) is currently working on a standard for Mobile IP. The main goals of the Mobile IP standard are that the system shall work within the TCP/IP protocol suite and provide Internet-wide mobility. The system shall also be transparent to higher layer protocols and allow hosts to keep their IP addresses as they migrate. In addition, no changes shall be required of non-mobile hosts and routers. It should be noted that a mobile terminal in this context does not necessarily mean a mobile terminal having a radio interface but a fixed terminal or user that changes its point of a attachment from one fixed network to another.
An example of such an Internet-type mobility protocol is the IP mobility (IP=Internet Protocol), which is the topic of standards RFC2002 to RFC2004 and RFC2290 by the Internet Engineering Task Force (IETF). These RFC standards are incorporated herein by reference. In short, IP mobility is a mechanism for providing a mobile user with telecommunications capability using an IP address. It enables Mobile Nodes to change their points of attachment in the Internet without changing their IP address. Thus it facilitates the communication of a Mobile Node and a correspondent host with the Mobile Node""s home address.
This Mobile IP protocol allows transparent routing of IP datagrams to Mobile Nodes in the Internet. Each Mobile Node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a Mobile Node is also associated with a care-of address, which provides information about its current point of attachment to the Internet. The protocol provides for registering the care-of address with a Home Agent. The Home Agent sends datagrams destined for the Mobile Node through a tunnel to the care-of address. After arriving at the end of the tunnel, each datagram is then delivered to the Mobile Node.
The Mobile IP protocol introduces the following new functional entities: a Mobile Node, a Home Agent and a Foreign Agent. A Mobile Node is a host or router that changes its point of attachment from one network or subnetwork to another. A Mobile Node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (constant) IP address, assuming link-layer connectivity to a point of attachment is available.
A Home Agent is a router on a Mobile Node""s home network which tunnels datagrams for delivery to the Mobile Node when it is away from home, and maintains current location information for the Mobile Node. A Foreign Agent is a router on a Mobile Node""s visited network which provides routing services to the Mobile Node while registered on that network. The Foreign Agent detunnels and delivers datagrams to the Mobile Node that were tunnelled by the Mobile Node""s Home Agent. For datagrams sent by a Mobile Node, the Foreign Agent may serve as a default router for registered Mobile Nodes.
Each Mobile Node is given a long-term IP address on a home network. This home address is administered in the same way as a xe2x80x9cpermanentxe2x80x9d IP address provided to a stationary host. When away from its home network, a xe2x80x9ccare-of addressxe2x80x9d is associated with the Mobile Node and reflects the Mobile Node""s current point of attachment. The Mobile Node typically uses its home address as the source address of all IP datagrams that it sends.
The care-of address is the termination point of a tunnel toward a Mobile Node, for datagrams forwarded to the Mobile Node while it is away from home. The protocol can use two different types of care-of address: a xe2x80x9cForeign Agent care-of addressxe2x80x9d is an address of a Foreign Agent with which the Mobile Node is registered, and a xe2x80x9cco-located care-of addressxe2x80x9d is an externally obtained local address which the Mobile Node has associated with one of its own network interfaces.
The Mobile IP protocol functions basically as follows: mobility agents (i.e., Foreign Agents and Home Agents) advertise their presence via Agent Advertisement messages. A Mobile Node may optionally solicit an Agent Advertisement message from any locally attached mobility agents through an Agent Solicitation message. A Mobile Node receives these Agent Advertisements and determines whether it is on its home network or a foreign network.
When the Mobile Node detects that it is located on its home network, it operates without mobility services. If returning to its home network from being registered elsewhere, the Mobile Node reregisters with its Home Agent, through exchange of a Registration Request and Registration Reply message. When a Mobile Node detects that it has moved to a foreign network, it obtains a care-of address on the foreign network. The care-of address can either be determined from a Foreign Agent""s advertisements (a Foreign Agent care-of address), or by some external assignment mechanism.
The Mobile Node operating away from home then registers its new care-of address with its Home Agent through exchange of a Registration Request and Registration Reply message with it, possibly via a Foreign Agent. Datagrams sent to the Mobile Node""s home address are then intercepted by its Home Agent, tunnelled by the Home Agent to the Mobile Node""s care-of address, received at the tunnel endpoint (either at a Foreign Agent or at the Mobile Node itself), and finally delivered to the Mobile Node. In the reverse direction, datagrams sent by the Mobile Node are generally delivered to their destination using standard IP routing mechanisms, not necessarily passing through the Home Agent.
When away from home, Mobile IP uses protocol tunnelling to hide a Mobile Node""s home address from intervening routers between its home network and its current location. The tunnel terminates at the Mobile Node""s care-of address. The care-of address must be an address to which datagrams can be delivered via conventional IP routing. At the care-of address, the original datagram is removed from the tunnel and delivered to the Mobile Node.
There are several problems still being addressed with systems employing current Mobile IP methods. In order to provide Mobile IP service to a Mobile Node, the Home Agent has to accept the Mobile IP registration request, validate it and return the Mobile IP registration reply to the Mobile Node indicating that either the Home Agent accepts or refuses to offer the Mobile IP service. Thus it can be seen that in order to ensure reliable Mobile IP service requires ensuring a reliable Home Agent.
One way to address this problem is to provide several Home Agents and distribute the number of registered Mobile Nodes between these Home Agents. In order to distribute the Mobile Nodes among the Home Agents, the network operator has to statically pre-assign a number of Mobile Nodes to a specific Home Agent. Since a Home Agent is statically pre-assigned to a number of Mobile Nodes by the network operator, no measures are taken to ensure that the traffic load handled by the Home Agent is balanced between the different Home Agents.
Considering that, managing all the Mobile Nodes and Home Agents pre-assigned proves to be an onerous task. It is difficult to manage all the Mobile Nodes in a large network by pre-assigning Mobile Nodes to a specific Home Agent and it won""t guarantee that the Mobile Nodes will be evenly registered among the Home Agents. One way to evenly distribute these Home Agents is by balancing the load between them. In order to distribute the Mobile Nodes optimally between the different Home Agents, the load information of each Home Agent on the network should be shared between them. Currently there is no mechanism that allows sharing this load information of each Home Agent with the other Home Agents.
In addition to the above problem, another problem exists when deploying multiple Home Agents with redundancy. Current systems which provide redundancy do so using hardware. However, some platforms on which Home Agent functionality will be implemented don""t provide hardware redundancy. In case of failure of the Home Agent in those systems the Mobile IP service will be interrupted until the failed Home Agent recovers. In addition, even in the systems providing hardware redundancy there exist no measures to ensure redundancy for the Home Agent if the hardware redundancy is not available.
The present invention relates to data communications in packet switched networks and more specifically to the mobility of terminals in networks implementing the Mobile Internet Protocol (MIP).
As can be seen above, there still exists disadvantages with current Mobile IP systems. Current systems typically deploy several Home Agents and provide for some level of redundancy among those Home Agents. The Mobile Nodes in the network are then distributed among these Home Agents.
Because the Home Agents are statically pre-assigned to a number of Mobile Nodes by the network operator, no measures are taken to ensure that the traffic load handled by the Home Agents is balanced between the different Home Agents.
In addition, the Mobile IP systems which provide for redundancy do so using hardware. No measures exist to ensure redundancy for failure in the assigned Home Agent if hardware redundancy is not available.
Accordingly, an object of the present invention is to solve or at least minimize the problems associated with the prior art IP mobility mechanisms. The object is achieved with a method which is characterized by what is disclosed in the attached independent claims. Preferred embodiments of the invention are disclosed in the attached dependent claims.
The present invention is designed to work in a packet switched network implementing mobility over the Internet, as exemplified by systems using the Mobile Internet Protocol (xe2x80x9cMIPxe2x80x9d). The network will have a number of Mobile Nodes attached to the network. Each Mobile Node will have an IP address and be attached to the network through a Home Agent. When visiting another network a Mobile Node will register with that network through a Foreign Agent. The network will provide a number of Home Agents through which the Mobile Node may register, although the Mobile Node will be statically configured to register with a given Home Agent.
In the method according to the present invention each Home Agent will store locally the load information from other Home Agents and will use load information and load information acknowledge messages to exchange load information with the other Home Agents.
The Mobile Node will send a Registration Request to the Foreign Agent with the statically configured address of its primary Home Agent. The Foreign Agent then forwards the request to this primary Home Agent. In certain situation the request for registration will not be completed due to e.g. failure of the primary Home Agent or where the network chooses balance the load on the network by registering the Mobile Node with another Home Agent having a lower load.
The Mobile Node then sends a Registration Request to the Foreign Agent with the address of a second, alternate, Home Agent. The Foreign Agent then forwards this request to the alternate Home Agent. If the alternate Home Agent accepts the request then it sends a reply to the Mobile Node and sets up a new mobility binding and establishes a tunnel between the Foreign Agent and second Home Agent.
There are two methods provided in the present invention to solve the two situations where the Mobile Node fails to register with its primary Home Agent. These problems occur more frequently in present systems, as discussed above, due to problems of hardware-only redundancy and lack of load balancing among Home Agents. The present invention suggests a method using Mobile IP Home Agent Load Balancing whereby a balanced distribution of Mobile Nodes among Home Agents is achieved.
The present invention also addresses the problems with hardware redundancy by providing for software redundancy to allow users to benefit from Mobile IP services even when a HA experiences failure. Two alternatives are proposed. According to a first solution an additional Mobile IP extension is added to the registration reply message which allows the Mobile Node to select, among those listed in the Mobile IP extension, a new secondary Home Agent to perform registration with in case the primary Home Agent fails. According to a second solution, a dedicated hot standby or shared redundancy Home Agent is called upon. The proposed solution, via the Home Agent software redundancy, thus allows for continuous Mobile IP services in case of Home Agent failure, even when the Home Agent platform does not provide hardware redundancy.
The present invention is not discussed in terms of any particular system. It is particularly applicable to applications in e.g. cellular, satellite, wireless local area networks (WLAN""s). However, it is not limited to these systems and may, in general, be used in any system which implements the Mobile IP having Mobile Nodes, Home Agents and Foreign Agents. Although the invention has been summarised above, the present invention is defined according to appended claims 1, 25, 26 and 27. Various embodiments are further defined in the dependent claims.